Regen Temps Challenge Vehicle Exhaust System Users

Managing the temperature demands of a catalytic converter regeneration (Regen)
event is a growing concern for mass transit engine service operators. Extremely
high temperatures associated with Regen events can pose dangers for vehicle
exhaust (VE) systems and their users. Everything from fan capacity to the
velocity of air in the flexible hoses that duct extremely high temperature
exhaust fumes away from diesel engine maintenance bays needs to be able to
mitigate temperatures that can exceed 1,600 F and cause safety problems.

“We were concerned that if the engine exhaust system went into the Regen mode
when the vehicle was in the garage, the existingexhaust hoses would not be able
to withstand the high temperature and may cause a fire,” says Dave Varner,
director of Bus Maintenance at the Maryland Transit Administration (MTA). So,
what did Maryland do? “We changed all exhaust hoses to high-temperature,” Varner
says. A complete facility-wide upgrade of MTA’s engine exhaust systems came at a
time when the transit system was able to replace all flexible exhaust hoses and
upgrade VE systems with those capable of ducting the 1,500 F and higher
temperatures, and MTA did so.

CEOs of transit agencies are directing their safety managers and facility
architects to look into how best to accommodate changes created by new,
higher-temperature engines and to meet the requirements of new regulations.
Private bus garage operators, too, are looking for technical answers to the
extremely high heat, safety and ventilation issues that arise from catalytic
converter regeneration that occurs during planned maintenance operations.

OEMs that offer full vehicle exhaust systems and design services to bus and
transit authorities are quick to point out that hoses capable of handling
extremely high temperatures are just a part of the solution for managing new,
high-performance engine exhausts. “Often, vehicle exhaust systems are not
designed by a person in our industry,” says Fred Imming, president of Car-Mon.
“Unfortunately, service managers want to use what they already have, as much as
possible,” Imming says.

“They really need to look beyond components to systems,” he suggests. “Vehicle
exhaust systems require a systems professional, not just a consulting engineer
with HVAC experience. The difference is that we are dealing with contaminated
air versus standard air for venting.”

Sizes, Fans and Pressures

System sizes, the number of drops, venting diameters, the right fans,
maintaining correct flow rates — they all have to be considered, Imming says.
“The best counsel that I can suggest is, you really need to contact a person
familiar with the requirements and materials available, and actually determine
which system fits your individual needs.

“You need to evaluate system performance in general. We’re systems guys, not
component guys,” Imming says of Car-Mon and similar OEMs companies.

Systems OEMs Share Views on Extreme Temps

Kyle Jefferson, VP of sales and engineering at Ventaire, echoes the need to have
exhaust fans properly sized to ensure that VE systems are not compromised by
extreme temperatures, and he goes a step beyond. “For existing systems, a
portion of all of the flexible hose may need to be upgraded to one that carries
a higher temperature rating.” Are there ways to economize?

“Yes,” says Jefferson. “The first 10 feet of flexible hose takes the brunt of
the heat since the exhaust gases cool quickly after they enter the exhaust
capture system. Hoses with different temperature ratings can be spliced together
with the section near the inlet carrying the highest temperature rating,” he
explains. “We supplied a system for a bus manufacturer that utilized 10 feet of
hose rated to 2,010 F coupled to 25 feet of hose rated to 1,200 F,” Jefferson
says to further illustrate the example.

“Another way to keep the cost of engine exhaust removal systems down is to
increase the volume of air moved by the fan,” Jefferson continues. “The fan can
be oversized to draw room temperature air into the system, which mixes with the
hot exhaust gases to keep the overall temperature to a level where
cost-effective components can be used,” he suggests.

Adding to the discussion, Monoxivent national sales manager Erik Swanson
endorses the idea of adding more ambient air into the system in order to keep it
cool, while suggesting other VE system changes, as well. “We may also add
high-temperature accessories to the exhaust fan such as heat slingers,
high-temperature paint and other suggestions,” Swanson explains.

“In an extreme case, where the vehicles may go into regeneration mode while
attached to the vehicle exhaust system, we could possibly recommend utilizing a
2,000 F flex hose,” he adds.

Toward a Safer Work Environment

Monoxivent’s Swanson looks to overall safety as part of the VE system
improvements that can enhance the working environment. “We can put
heat-resistant handles on our tailpipe adaptors to help prevent the mechanics
from getting burned,” he suggests. “Mechanics have to keep in mind that today’s
engines are running hotter, which creates more heat in the vehicle exhaust
system. They must exercise care when removing the VE system from the vehicle,
because it may be hot, especially right after the vehicle is shut down,” Swanson
adds. He even suggests that vehicles be pulled outdoors to conduct certain
engine tests that will definitely create high exhaust gas temperatures, and that
the vehicle be disconnected from the VE system to do so.

Combining Old Engines with New Engine Maintenance Ops

“For the time being, service managers could designate one or two work bays of
their facility for the service of new vehicles,” Swanson suggests. “These bays
could be outfitted or retrofitted with higher temperature, higher air volume
exhaust extraction equipment and leave the rest of the facility as is,” he
reasons. “As more of the higher temp engines are introduced into the fleet, more
bays can be retrofitted with high-temperature exhaust hoses and equipment,”
Swanson concludes.

VE System Design Refinements Sense Load Capacity

Shawn Smith, vice president of Operations at Plymovent, Cranbury, N.J., urges a
thorough understanding of usage capacity for the VE system, including
considering the percentage of drops that will be in use at a given time.
“Service managers need to get a clear snapshot of all types of vehicles that
move through the service area,” he recommends. “Planning should include a
temperature monitor at each of the extraction points to ensure that no vehicle
in maintenance reaches or exceeds an approved temperature level,” Smith says.

Outsourcing Regeneration Servicing

Car-Mon’s president, Fred Imming, points to an industry trend that is
influencing maintenance of higher temperature bus engines: outsourcing
maintenance services to engine manufacturers. The Chicago Transit Authority
(CTA) designates two bays in at least one of its bus barns for regeneration and
subcontracts the maintenance work out to engine companies, he says. “Normally,
they have two people from Cummins designated to come out and evaluate the
catalytic convertor maintenance,” Imming says. “You have to plug regeneration by
laptop link to a computer program,” for scheduled maintenance, he explains.
Otherwise, catalytic converter regeneration can occur on the road, he adds.

All the more reason to have VE systems checked for extremely high-temperature
performance ability in those bus bays where regeneration maintenance is
scheduled, Imming suggests. In a world where technical improvements in engines
are taking place, engine service managers need to review the basics and ante up
for vehicle exhaust systems that will match the oncoming requirements while
providing improved safety and security in their operations.

Management of exhaust is one of the key components to any service function. New
VE systems solve a practical problem and they are affordable and available
today.